Abstract:
Biodiesel from waste cooking oil (WCO) is an environment friendly
renewable energy source. Generally, NaOH or KOH are used as catalysts to
produce biodiesel from vegetable oil via transesterification reaction.
Although, these homogeneous catalysts have high catalytic activity they have
certain drawbacks such as difficulty in catalyst separation, high soap
formation and requirement of large amount of water to wash biodiesel product.
Alternatively, CaO has been used as catalyst for this reaction but its efficiency
is poor. Coral rubbles are abundantly found in southern coast of Sri Lanka and
calcinating them to 900 ⁰C yield CaO rich coral rubble catalyst (CRC). In this
research, the catalytic performance of CRCs against the transesterification
reaction to produce biodiesel and its improved efficiency by incorporating rice
husk silica was tested. Rice husk contains around 20% of biogenic silica.
Therefore, initially, silica was extracted from pyrolyzed rice husk ash via
alkaline extraction. Subsequently, SiO2 was incorporated to the CRC via wet
impregnation. Catalytic efficiency of CRCs with different weight percentages
of silica was investigated. Accordingly, 20% wt silica loaded CRC showed the
highest catalytic performance. Optimum biodiesel yield was obtained at a
methanol to oil molar ratio of 18:1 and catalyst dosage of 8% wt at 60 ⁰C for
2 hrs. Catalyst reusability was tested for 5 runs and it has shown a significant
yield over 75%. Fourier transform infrared spectroscopic (FTIR) data revealed
the presence of Ca-O-Si bond in silica incorporated CRCs. pH, density, acid
value and saponification value of the produced biodiesel were tested and they
were within the accepted ASTM limits.
